This invention relates in general to sample inspection systems and, in particular, to an improved inspection system with good sensitivity for particles as well as crystal-originated-particles (COPs). COPs are surface breaking defects in semiconductor wafers which have been classified as particles due to inability of conventional inspection systems to distinguish them from real particles.
Systems for inspecting unpatterned wafers or bare wafers have been proposed. See for example, PCT Pat. application No. PCT/US96/15354, filed on Sep. 25, 1996, entitled xe2x80x9cImproved System for Surface Inspection.xe2x80x9d Systems such as those described in the above-referenced application are useful for many applications, including the inspection of bare or unpatterned semiconductor wafers. Nevertheless, it may be desirable to provide improved sample inspection tools which may be used for inspecting not only bare or unpatterned wafers but also rough films. Another issue which has great significance in wafer inspection is that of COPs. These are surface breaking defects in the wafer. According to some opinions in the wafer inspection community, such defects can cause potential detriments to the performance of semiconductor chips made from wafers with such defects. It is, therefore, desirable to provide an improved sample inspection system capable of detecting COPs and distinguishing COPs from particles.
This invention is based on the observation that anomaly detection employing an oblique illumination beam is much more sensitive to particles than to COPs, whereas in anomaly detection employing an illumination beam normal to the surface, the difference in sensitivity to surface particles and COPs is not as pronounced. Anomaly detection employing both an oblique illumination beam and a normal illumination beam can then be used to distinguish between particles and COPs.
One aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising first means for directing a first beam of radiation along a first path onto a surface of the sample; second means for directing a second beam of radiation along a second path onto a surface of the sample and a first detector. The system further comprises means including a mirrored surface for receiving scattered radiation from the sample surface and originating from the first and second beams and for focusing the scattered radiation to said first detector.
Another aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising first means for directing a first beam of radiation along a first path onto a surface of a sample; second means for directing a second beam of radiation along a second path onto a surface of the sample, said first and second beams producing respectively a first and a second illuminated spot on the sample surface, said first and second illuminated spots separated by an offset. The system further comprises a detector and means for receiving scattered radiation from the first and second illuminated spots and for focusing the scattered radiation to said detector.
One more aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising a source supplying a beam of radiation at a first and a second wavelength; and means for converting the radiation beam supplied by the source into a first beam at a first wavelength along a first path and a second beam at a second wavelength along a second path onto a surface of a sample. The system further comprises a first detector detecting radiation at the first wavelength and a second detector detecting radiation at the second wavelength; and means for receiving scattered radiation from the sample surface and originating from the first and second beams and for focusing the scattered radiation to said detectors.
Yet another aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising a source supplying a radiation beam; a switch that causes the radiation beam from the source to be transmitted towards the sample surface alternately along a first path and a second path; a detector and means for receiving scattered radiation from the sample surface and originating from the beam along the first and second paths and for focusing the scattered radiation to said detector.
Another aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising means for directing at least one beam of radiation along a path onto a spot on a surface of the sample; a first detector and means for receiving scattered radiation from the sample surface and originating from the at least one beam and for focusing the scattered radiation to said first detector for sensing anomalies. The system further comprises a second, position sensitive, detector detecting a specular reflection of said at least one beam in order to detect any change in height of the surface at a spot; and means for altering the path of the at least one beam in response to the detected change in height of the surface of the spot to reduce position error of the spot caused by change in height of the surface of the spot.
Still another aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising means for directing at least one beam of radiation along a path onto a spot on a surface of the sample; a first detector and means for collecting scattered radiation from the sample surface and originating from the at least one beam and for conveying the scattered radiation to said first detector for sensing anomalies. The system further comprises a spatial filter between the first detector and the collecting and conveying means blocking scattered radiation towards the detector except for at least one area having a wedge shape.
One more aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising directing a first beam of radiation along a first path onto a surface of the sample; directing a second beam of radiation along a second path onto a sample of the surface; employing a mirrored surface for receiving scattered radiation from the sample surface and originating from the first and second beams and focusing the scattered radiation to a first detector.
Yet another aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising directing a first beam of radiation along a first path onto a surface of the sample; directing a second beam of radiation along a second path onto a surface of the sample, said first and second beams producing respectively a first and a second illuminated spot on the sample surface, said first and second illuminated spots separated by an offset. The method further comprises receiving scattered radiation from the first and second illuminated spots and for focusing the scattered radiation to a detector.
An additional aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising supplying a beam of radiation of a first and a second wavelength; converting the radiation beam into a first beam at a first wavelength along a first path and a second beam at a second wavelength along a second path, said two beams directed towards a surface of the sample. The method further comprises collecting scattered radiation from the sample surface and originating from the first and second beams, focusing the collected scattered radiation to one or more detectors, and detecting radiation at the first and second wavelengths by means of said detectors.
Yet another aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising supplying a radiation beam, switching alternately the radiation beam between a first and a second path towards a surface of the sample, receiving scattered radiation from the sample surface and originating from the beam along the first and second paths, and focusing the scattered radiation to a detector.
Another aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising directing at least one beam of radiation along a path onto a spot on the surface of the sample; collecting scattered radiation from the sample surface and originating from the at least one beam, and focusing the collected scattered radiation to a first detector for sensing anomalies. The method further comprises detecting a specular reflection of said at least one beam in order to detect any change in height of the surface at the spot and altering the path of the at least one beam in response to the detected change in height of the surface of the spot to reduce position error of the spot caused by change in height of the surface of the spot.
One more aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising directing at least one beam of radiation along a path onto a spot on a surface of the sample; collecting scattered radiation from the sample surface and originating from the at least one beam, conveying the scattered radiation to a first detector for sensing anomalies, and blocking scattered radiation towards the detector except for at least one area having a wedge shape.
Still another aspect of the invention is directed towards an optical system for detecting anomalies of a sample, comprising means for directing a beam of radiation along a path at an oblique angle to a surface of the sample; a detector and means including a curved mirrored surface for collecting scattered radiation from the sample surface and originating from the beam and for focusing the scattered radiation to said detector.
One more aspect of the invention is directed towards an optical method for detecting anomalies of a sample, comprising directing a beam of radiation along a path at an oblique angle to a surface of the sample; providing a curved mirrored surface to collect scattered radiation from the sample surface and originating from the beam, and focusing the scattered radiation from the mirrored surface to a detector to detect anomalies of the sample.